Using MERGE in SQL Server to insert, update and delete at the same time

Beginning with SQL Server 2008, now you can use MERGE SQL command to perform these operations in a single statement. This new command is similar to the UPSERT (fusion of the words UPDATE and INSERT.) command of Oracle; it inserts rows that don’t exist and updates the rows that do exist. With the introduction of the MERGE SQL command, developers can more effectively handle common data warehousing scenarios, like checking whether a row exists, and then executing an insert or update or delete.

The MERGE statement basically merges data from a source result set to a target table based on a condition that you specify and if the data from the source already exists in the target or not. The new SQL command combines the sequence of conditional INSERT, UPDATE and DELETE commands in a single atomic statement, depending on the existence of a record. The new MERGE SQL command looks like as below:

SYntex :-
MERGE <target_table> [AS TARGET]
USING <table_source> [AS SOURCE] ON <search_condition>
[WHEN MATCHED THEN <merge_matched>]
[WHEN NOT MATCHED [BY TARGET] THEN <merge_not_matched>]
[WHEN NOT MATCHED BY SOURCE THEN <merge_ matched=""> ]

Example:-

--Create a target table
CREATE TABLE Products
(
ProductID INT PRIMARY KEY,
ProductName VARCHAR(100),
Rate MONEY
)
GO
--Insert records into target table
INSERT INTO Products
VALUES
(1, 'Tea', 10.00),
(2, 'Coffee', 20.00),
(3, 'Muffin', 30.00),
(4, 'Biscuit', 40.00)
GO
--Create source table
CREATE TABLE UpdatedProducts
(
ProductID INT PRIMARY KEY,
ProductName VARCHAR(100),
Rate MONEY
)
GO
--Insert records into source table
INSERT INTO UpdatedProducts
VALUES
(1, 'Tea', 10.00),
(2, 'Coffee', 25.00),
(3, 'Muffin', 35.00),
(5, 'Pizza', 60.00)
GO


--Synchronize the target table with
--refreshed data from source table
MERGE Products AS TARGET
USING UpdatedProducts AS SOURCE ON (TARGET.ProductID = SOURCE.ProductID)
--When records are matched, update the records if there is any change
WHEN MATCHED AND TARGET.ProductName <> SOURCE.ProductName OR TARGET.Rate <> SOURCE.Rate THEN
UPDATE SET TARGET.ProductName = SOURCE.ProductName, TARGET.Rate = SOURCE.Rate
--When no records are matched, insert the incoming records from source table to target table
WHEN NOT MATCHED BY TARGET THEN
INSERT (ProductID, ProductName, Rate) VALUES (SOURCE.ProductID, SOURCE.ProductName, SOURCE.Rate)
--When there is a row that exists in target table and
--same record does not exist in source table
--then delete this record from target table
WHEN NOT MATCHED BY SOURCE THEN
DELETE
--$action specifies a column of type nvarchar(10)
--in the OUTPUT clause that returns one of three
--values for each row: 'INSERT', 'UPDATE', or 'DELETE',
--according to the action that was performed on that row
OUTPUT $action, DELETED.ProductID AS TargetProductID, DELETED.ProductName AS TargetProductName, DELETED.Rate AS TargetRate,
INSERTED.ProductID AS SourceProductID, INSERTED.ProductName AS SourceProductName, INSERTED.Rate AS SourceRate;
SELECT @@ROWCOUNT;
GO